<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
    div{
        width: 300px;
      height: 300px;
      padding: 10px;
      margin: 20px;
      border: 5px solid blue;
      /* box-sizing: border-box; 要求浏览器以IE盒子模型来加载盒子 */
      /* box-sizing: border-box; */
      /*要求浏览器以标准盒子模型来加载盒子*/

 }
    </style>
</head>
<body>
    <div>盒模型</div>
</body>
</html>